1. Field of the Invention
The invention relates to a gear-type machine for liquids or gases comprising a housing containing a gear chamber having inlet and outlet openings, an internally toothed ring gear arranged in the gear chamber and a pinion which is rotatably arranged within the ring gear in the housing and which has one tooth less than the ring gear, meshes with the latter and on rotation forms between its teeth and the teeth of the ring gear revolving, expanding and diminishing fluid cells which conduct fluid from the inlet to the outlet, the teeth heads of the pinion and the teeth gaps of the ring gear having the form of epicycloids which are formed by rolling of a first generating circle on the pitch circle of the pinion and ring gear, the teeth gaps of the pinion and the teeth heads of the ring gear furthermore having the form of hypocycloids which are formed by rolling of a second generating circle on the pitch circle of the pinion and ring gear respectively, and finally the radius of the first generating circle being different to the radius of the second generating circle.
The gear-type machine according to the invention may be used both as pump for liquids or gases and as motor driven by pressurized liquids or gases. However, the preferred field of use of the invention is as liquid pump. In the following description and in the claims, for the sake of simplicity, reference will be made only to fluids, meaning preferably liquids. In the claims the term fluid is therefore likewise intended to cover gases and liquids as well.
The following explanation of the invention will be made solely with reference to a pump for liquids.
The gear-type machine according to the invention may be one in which the ring gear is fixedly arranged in the housing, the pinion then rotating about the crank arm of a shaft which is arranged centrally with respect to the internal toothing of the pinion. However, the machine according to the invention is preferably one in which the ring gear revolves in the gear chamber and the pinion mounted eccentrically with respect to the axis of the ring gear and gear chamber rotates with a stationary shaft or about such an axis. The main field of use of the invention is as a machine constructed as internal ring gear pump for lubricating or hydraulic fluid for internal-combustion engines and automatic transmissions where delivery pressures of up to a maximum of 30 bar can occur. For this use, in which the pump pinion is preferably arranged in an extension of the crankshaft of the engine or the main shaft of the gearbox or is carried by said shaft, internal ring gear pumps have proved to be quiet low-vibration pumps. However, due to the constantly improving quietness of engines and transmissions constantly higher demands are being made on the quietness of such pumps.
2. Description of the Prior Art
Most known constructed internal gear-type pumps or ring gear pumps for internal-combustion engines and automatic motor vehicle transmissions operate with trochoid toothings in which the teeth flanks of the hollow gear or the pinion are limited by circular arcs and the counter wheel is defined by non-slip rolling in the toothing of the other wheel fixed by the arcs.
Gear-type pumps of the type improved by the invention have been known for a long time, for example from GB-PS 233,423 of the year 1925, or the publication "Kinematics of Gerotors" by Myron S. Hill, likewise originating in the twenties. The modern use of cycloid toothing for the aforementioned purpose in internal-combustion engine and automatic transmissions is described in Applicants' DE-PS 3,938,346. The pump according to this German patent employs the excellent kinematic properties of teeth and teeth gaps having a complete cycloid contour in an internal ring gear pump with a teeth number difference of one for mounting the ring gear with its toothing on that of the pinion which is carried by the crankshaft of the engine or the main shaft of the automatic gearbox. In this manner the relatively pronounced radial movement of the crankshaft can be compensated in that the peripheral mounting of the ring gear is chosen with adequate clearance for this compensation. It is equally possible to mount the ring gear with little play and then provide a correspondingly large play between the shaft bearing the pinion and the pinion, the pinion then being mounted with its toothing in that of the ring gear.
Such pumps represent a preferred field of use of the present invention.
For the undesired noise development and the resulting drop in efficiency of the known pumps, pressure pulsations, i.e. delivery flow pulsations, are primarily responsible, as well as the knocking of the teeth together in the radial and tangential direction. The delivery flow pulsations are intensified by squeeze oil pressure peaks which lead to oscillations in the gear running set. Cavitation noises also act in the same sense; they arise primarily due to the breaking down of liquid vapour bubbles in the region of the pressure chamber of the pump.